Oscillation production



PATENT oFFIcE.

RAYMOND A. HEISING, OF EAST ORANGE, NEW

TRIC COMPANY, INCORPORATED, 013 NEW JERSEY,'ASSIGNOR 'I'O WESTERN ELEC- YORK, N. Y., A CORPOBATION OF NEW O'SCILLA'IION PRODUCTION.

Application filed January 20, 1920.

The present invention relates to the transmission of impulses through a space discharge device at high efliciency. The invention is particularly applicable to radio or high frequency transmitting systems, or to space discharge systems involving considerable power.

A specific application of the invention is to oscillation generators of the type in which a resonant circuit is set into oscillation and is kept oscillating by periodically impulsing or exciting the circuit in synchronism with the natural or free oscillations of the circuit. A generator of this general type is disclosed in my prior Patent No. 1,240,206, granted September 18, 1917. lln that patent mechanical contact-making means is provided for connecting and disconnecting a source of voltage periodically to and-from an oscillatory circuit in which the oscillationsare produced. The present invention, while making use of the same broad principles of converting energy of current impacts or shock impulses into sustained oscillatory currents, instead of mechanically applying and removing the source of voltage, employs a novel method and means for accomplishing this function electrically as will presently be described.

One of the objects of'the present inventionis to amplify or repeat electric oscillations at high electrical elhciency.

According to the invention the exciting im-. pulses are delivered to the oscillatory circuit through a discharge device which may be of well known type and in which the large current pulses are controlled by relatively small fluctuations of an applied voltage. These controlling voltage fluctuations may act upon the third or grid electrode of the discharge device and preferably do not contribute any energy to the oscillation producing circuit. There are, in reality, two circuits besides the oscillatory circuit, one of which is the control circuit and the other of which is the energysupplying circuit for the oscillatory circuit.

These circuits may be separate or may'have portions in common as will appear later on. lln fact the invention may employ an an1pl1- tier or repeater of the usual vacuum tube type which is preferably constructed in a rugged manner if large power is to be handled. The

amplifying action taking, place differs from that occurring in the usual form of vacuum Serial No. 352,814.

tube amplifier of the prior art in which the space current is continuously transmitted through the tube. The device of the present invention is made to act in the manner of a trigger arrangement whereby the impressed voltage releases for an instant a large amount ofenergy for impacting or shock exciting the oscillatory circuit. Except during the time of impact, no space current passes through the device, and no energy is transmitted to the oscillatory circuit.

The nature and objects of the invention will better be understood from the following detailed description together with the drawings of which Fig. 1 is a diagrammatic circuit drawing of one form which the invention may take; Fig. 2 shows curves explanatory of the action of the circuit of Fig. 1 and Fig. 3 shows an alternative circuit arrangement.

In Fig. 1 the electronic or device 1 may be an amplifier of the usual construction, preferably such as will handle relatively large amounts of power. It may consist of a highly evacuated enclosure containing a hot filament 2', a plate or anode 3, and a grid or impedance-control element 4:. The grid circuit contains a battery 5 for fixing the normal grid potential relative to its filament, and the coil 6, shown as the secondary of the transforn'ier, the primary of which is supplied with current from alternator 7. The output or plate circuit contains the source 8 of space current voltage, which in this case is preferably of large value, and the primary winding 9 of the resonant transformer. The invention is not limited to the use of direct current for the plate circuit supply, and, in fact, it may be desirable at times to use other kinds of current supply, such for example as cycle current from power supply circuits, or currents of other frequencies. The secondary 10 of the output transformer is included in the oscillatory circuit which in this case is assumed to be the load circuit containing also condenser 11 and resistance 12. The circuit 10, 11, 12 is preferably tuned to the frequency of the alternator which may or may not deliver a wave of sine form. So far as has been indicated up to this point the arrangement would appear to consist of a tuned circuit, an oscillator for feeding into the circuit and an amplifier connected between. The relation of the different elements and the acionic discharge tion of this circuit are, however,.radically different from the case of an ordinary amplifier circuit and the effects produced are quite different from those associated with amplification or contemplated in amplifying circuits of the prior art as will presently be described. 7 i

If, as has been the usual practice heretofore, the sources 8 and 5 were so proportioned as to give a normal steady transmission of current through the tube and if the'point corresponding to this normal current should lie near the middle portion of, a substantially linear region of the tube characteristic, and if, in addition, the voltage of the source 7 were sufliciently small not to carry the current outside the limits of this linear portion of the characteristic curve, the wave from source 7 would be repeated substantially true to form, and, assuming this Wave to be sinusoidal, the amplified wave would produce in the circuit 10, 11, 12 current to which the circuit is resonant. The efliciency in this case would, however, be less than fifty percent and' probably would be about thirty-five percent, on the basis of alternating current.

power output to total power input plate circuit.

If the impedance of the tube is varied between zero and infinity in such a manner as to give an alternating current of the foigm -2 where R is the external ohmic resistance (due to the coupled tuned circuit) through in the .1 =11 (1 +sin wt), the power output is which the alternating current must pass, and

the ideal efficiency in such a case cannot exceed fifty percent as may be seen from the following considerations. A current of this form may obviously be assumed to be produced whether the alternating current eir-' cuit is coupled to the plate circuit conductively, inductively 0r ca acitively. In any of these cases the total p ate current may be looked upon as having a direct current com onent which flows in the direct, current ranch and an alternating current component.

in the alternating current circuit, and at the instant of maximum total current each component is equal to A as is evident from the equation. The power supplied tothe plate circuit isEI which is equal to E A (1 sin (al "where E is the voltage of the battery 8. For a complete cycle, this mtegrates to EA.

Since the efficiency is computed on a basis .of alternating current output as compared with the total input power to the plate circuit, itis convenient to express E 1n terms of the maximum alternating current and the mum value of current occurs when the tube impedance is nearest to zero. In the case of a single frequency, such as is here being considered, the output circuit of Fig. 1 is, in accordance with ordinary transformer theory. equivalent to a single large inductance coil connected in the plate circuit in the same manner as coil 9 and shunted by a circuit from which the direct current is excluded but which contains a resistance equivalent in Value to the alternating current resistance of the circuit of Fig. 1 as seen from the primary circuit 3, 9, 8. In the case of such an equivalent circuit, at the instant when the impedance of the tube drops to zero, the entire potential of battery 8 is applied to the terminals of the resistance R and the alternating current component is at its peak value A. The alternating current drop of potential at this instant is AR which is equal and opposite to E, the potential of the plate buttery. This relation between E and the alternating potential drop AR holds, under the conditions assumed, whichever type of coupling mentioned above is used. The efliciency on the basis of the ratio of the alternating current output and the total power supplied to the plate circuit is given by Since the tube impedance never becomes zero, however, this efficiency is never realized in practice.

If the impedance of the tube could be varied instantly from zero to infinity and from infinity to zero, the efficiency would be Gb since no power is lost in the tube at either of these impedance values. The output current would then have a rectangular wave form if the external impedance were a pure resistance for all frequencies and would ha re some logarithmic curvilinear form for a tuned circuit as shown in Fig. 1. This represents avast difference in efficiency over the case in which the impedance varies between these same'limits in such a manner as to produce a current having a sine wave form as is seen from the ideal efficiencies in the two cases. The current wave varied by sudden changes in tube resistance may be considered as an interrupted direct current and the tube when used as such an interrupter not only operates at a high efficiency as regards plate losses, but is controlled in a very simple manner and by the application of a wave of coinparatively small voltage. This control wave may be of very low power since the grid curren-t' s' practically zero.

To obtain this interrupting action of'the tube the conditions are very different from those assumed above in the case where the tube acts only as an amplifier. The source 8 should be of large voltage and the potential loo , the tube.

the grid less negative than the value E ourof source 5 should be such as to make the grid so far negative that there is normally substantially zero space current. This is indicated in Fig. 2 where E represents the potential of source 5 (shown below the line of zero potential since it is negative) E indicates similarly the voltage of source 8 and I shows the cur.- rent through the tube as a result of voltage impressed from source 7. This applied voltage is indicated by the sinusoidal curve 19 drawn about the lit axis and the corresponding variations in plate voltage are shown by the curve 20 about the E, axis. When the grid potential is E or still more negative there is seen to be no current flow through As the .wave from source 7 makes rent begins toflow and the potential differ-- ence between the filament and the plate gradually falls. The current is therefore prefer ably interrupted each cycle for substantially one-half the period or more and the trans mitted current has a rapid rate of change bothrising and falling.

The Wave shape of the impulsedepends upon the nature of the attached circuit, the value of 1B)., and the magnitude of the voltage impressed from generator 7 on the grid. Uurves 21 and 22 show two forms besides the rectangular form mentioned above. Full line curve 21 represents an extreme case, (the reason for it being given later) which contains two impulses per cycle not uniformly spaced. The two separate and distinct impulses of each pair are so close together (coming within a half cycle) that they act as one impulse to produce a current in the tuned circuit 10, 11 and 12 ofthe frequency from the source 7. Dotted curve 22 is an impulse wave form when the coupling 9-40 and voltage applied on member l'are both smaller than that required to produce the extreme .case.

The reason that the current half-cycle impulse is deformed into two pulses is that they plate to filament difference of potential approaches zero or reverses during a small portion of the cycle. This is indicated by the curve of plate voltage shown, the peak value of which is greater than 2E During the time that the plate voltage is Zero or negative, there is no driving voltage for the current I. Also, if the grid potential rises above the value represented by the line 24, it fails to increase the space current and actually will re duce it if the plate potential is small. With a large input to the grid and with the plate potential having a somewhat smaller value such as that shown'by the curve 23, it is also possible for the split impulse to occur. By making the .plate variations somewhat as shown by curve 23 (for half-cycleonly) and the grid variations not above line 24, the current curve may be made to assume the form of the dotted line 22 in the corresponding halfcycle. The line 24 is assumed to represent the smallest value of positive grid potential beyond which any increase in grid potential in the positive direction produces no further increase in plate current. This value will differ with different tubes and with different plate voltages and may be determined experimentally for any given case in known manner.

'It is not necessary to provide a separate source for the control voltage. In fact an oscillator of any one of several well-known types can be made to operate at high efficiency by making use of the principles of shock excitation by completely interrupting the plate current in accordance with the present invention. An oscillator of known type which has been found adapted to this use is shown in Fig. 3. In this case no separate source of normal grid potential corresponding to battery 5 of the other figure is used, but the resistance 13 acting as a grid leak furnishes the necessary negative grid potential although this could be replaced by a source similar to 5 if desired. The oscillatory circuit consists of the coils 14 and 15 and the variable condenser 16. A. large blocking condenser 17 is included in this circuit; The plate battery 8 is shown provided witha shunting condenser 18. An oscillator of this type has given in actual trial efficiencies considerably in excess of fifty percent when the plate current was controlled as above explalned so as to produce shock excitation of the oscillatory circuit.

In place of the grid battery 5 in the circuit of Fig. 1, a leak resistance similar to 13 may be employed if desired. The generator indicated at 7 may, of course, be a machine or an oscillating thermionic tube or any other suitable type. Also instead of-a generator at the point 7, there may be substituted other means for exciting the circuit such as a source of current with an interrupter or commutator, or a quenched-spark gap 01' the like, but a generator of the oscillating tube type is preferred on account of its simplicity and ease of control at any desired frequency.

The present invention is a continuation in part of my prior application, Serial No. 114,777, filed August 14, 1916, in which the claims are directed to wave modulation whereas the claims of the present application are directed broadly to transmission through a space discharge device at high efficiency and are not concerned primarily with the problem of modulation since they define an invention which may find embodiment not only in modulating systems but in amplifiers, generators and space discharge systems generally. V y

The invention is not to be limited to the specific forms shown and described, but its scope is defined in the appended claims.

What is claimed is: 1. The method of operating at high efiiciency avacuum tube device oscillation producing system in which the frequency of the oscillations produced is determined by the free period of an oscillatory circuit, which method comprises controlling the impedance of the discharge device to interrupt the anode current each 0 cle for at least one-half the period of osci lation and utilizing the current transmitted through the device to impulse the oscillatory circuit in synchronism with the oscillations in said circuit.

2. The method of operating at high efliciency an oscillation producing system having an oscillatory circuit, a source of current, and an electronic discharge space interposed between the oscillatory circuit and the source of current, which comprises acting electrically upon said discharge space to interrupt said current each cycle for at least one-half the period of oscillation of said circuit and applying the intervening space current impulses to said oscillatory circuit in synchronism with the natural oscillations of said circuit.

'- 3. The method of operating at high efficiency a vacuum tube discharge oscillation producing system of the type employing a discharge tube having a grid or control element for controlling the anode current and an oscillatory circuit for determining the period of oscillations produced, which method 'comprises applying to the grid a substantially sinusoidal control wave and maintaining the steady potential about which the grid potential oscillates and the amplitude of the sinusoidal grid potential oscillations at such values relative to the anode voltage of the tube that the anode current is interrupted each cycle for at least half a period and the discharge current through the tube in rising toward its peak value and back to zero has a steeper wave front than the corresponding portion of said control wave.

4. The method of operating at high eflicicncy an oscillation reducing system of the type employing an eiectron discharge device having an electron emitting cathode, an oscillatory circuit associated therewith and a grid or control element for acting upon the space discharge in said device, which method comprises applying periodically negative potential to said grid of such a value that the discharge device transmits no current for at least one-half period in each cycle of the oscillations produced, alternating with said negative potential a positive potential to cause periodicimpulses of current through saiddischarge device in synchronism with the natural period of the-osci1lations produced, and utilizing said impulses to give impact excitation to the oscillatory circuit.

5. An oscillation system having an oscillatory circuit and a discharge device for energizing said circuit, said device having a cathode, an anode and agrid, and means including a source of voltage variations and a grid-biasing element for periodically varying the potential of said grid about a mean value so far negative that at that value the device transmits substantially no current, to

make the conductivity of said device alternately momentarily high and low whereby said oscillatory circuit is energized by impulse excitation and energy losses due to normally transmitted discharge current are substantially avoided.

6. In an oscillation producing system, an oscillatory circuit, a source of current, a discharge device for transmitting energy from said source to said circuit having means for maintaining a discharge path, means controlled by an oscillatory electromotive force in -synchronism with the oscillations produced for acting upon said path to interrupt the transmission of energy between said source and said circuit in each cycle of the oscillations for at least one-half the period of oscillation and for'alternately transmitting pulses of energy from said source to said circuit to maintain said circuit in a state of continuous oscillation whereby energy losses in said discharge path are substantially avoided between the successive energy pulses.

7. In an oscillation generating system an oscillatory circuit, a source of current for supplying energy to keep said circuit continuously oscillating, a space discharge tube for controlling transmission of current to said circuit having a grid normally poled to preventtransmission of current from said source to said circuit and means for varying the grid potential in synchronism with the 100 oscillations produced to cause sudden discharges of current into said circuit of a durationnot greater than one-half the period of oscillation of the circuit whereby the .energy losses resulting from the flow of space current are substantially avoided for atleast one-half period in each cycle of the nating electromotive force waves of a uni- 11o directionally conducting element associated therewith comprising an electron discharge device having a cathode and an anode, a source of current connected between saidv cathode and anode, and means acting 0011- stantly upon said device and normally of suflieient magnitude to prevent an electron discharge between said cathode and anode,

to cause said device to operate to repeat portions of the wave from said source of one polarity only whereby the energy losses resulting from an electron discharge between said cathode and anode are avoided during the intervals between the portions of said wave that are'repeated.

9. An electron discharge device comprising a cathode, an anode and a control element, a circuit including a space current source connected to said cathode and anode, an input circuit including a permanently 130 connected sourcepf substantially constant potential, and means for applying a high frequency electromotive force wave to said in at circuit, said constant potential source being of such voltage that when acting alone in said input circuit it substantially prevents electron ilow in said device whereby energy losses resulting from the flow of space current in said device are substantially avoided at all times except during the instants when theapplied grid potentials affect the potential of the grid in the positive direction.

10. An amplifier of the space currenttype having a cathode, an anode, and a grid, a source of space current associated with'said anode and cathode, means to supply a sub stantially constant electromotive force between said cathode and grid of sufficient magnitude when acting alone on said grid to prevent the flow of space current between said cathode and said anode, and means for also applying'alternating electromotive force waves to the grid, whereby said amplifier operates to amplify portions of the waves of one polarity only and the energy losses resulting from the flow of space current in said device between the said portions of the wave that are amplified are avoided.

11. The method of operating an electron discharge device having a cathode and an anode and a source of current connected between the cathode and anode, to produce and transmit current impulse at-high frequency, comprising normally continuously preventing an electron discharge between said cathode and anode, and applying to said device an alternating electromotive force wave to cause a discharge to occur between said cathode and a'node in alternate half-cycles only of the applied wave, and of a duration at least as short as one half the period of the applied wave.

12. The method of operating an electron discharge device having an input and an output circuit and a source of space discharge current connected in'said output circuit, to

produce and transmit unidirectional current impulses at high efiiciency, comprising applying-to the input circuit a unidirectional source of electromotive force suflicient in the absence of other applied electromotive forces to prevent any flow of current in the output circuit from said source of space discharge current, and simultaneously applying to said input circuit an alternating electromotive force wave for causing impulses of current to flow in the output circuit of a duration of flow at least as short as one half the period of the applied electromotive force wave.

13. In combination, a'space discharge device having a cathode, an anode and a grid or control element, a source of space discharge current connected to the cathode and anode, a source of negative grid polarizing potential connected to the "rid of such magnitude as to prevent the disc arge of space current between the cathode and anode in the absence of other applied-volta es than those from said two sources, whereby energy losses arising from normally flowing space current are avoided, means to apply periodic positive po tential variations to the gridwhereby periodic current discharges occur between the cath- -ode and anode only during the instants of arising 'from normally flowing space current are avoided, a source of electromotive force waves applied to the grid, and an output circuit associated with the cathode and anode tuned to the frequency of the said wave applied to the grid. 15. In a high frequency generator, a threeelectrode vacuum tube comprising a cathode, an anode, and a control electrode, an oscillatory circuit comprising inductance and capacity, said anode and control electrode being connected respectively to oints in said oscillatory circuit of unequal liigh frequency potential, said cathode being connected to a point in said oscillatory circuit, the potential of which is always intermediate of the poten-' tials of said first mentioned points, and a source of direct current having its negative terminal connected to said cathode and its positive terminal connected to a point in said oscillatory circuit which is constantly at substantially the same hi h frequency potential as the aforementione point to which said cathode is connected,'said source of direct current being included in a direct current circuit between said anode and cathode.

In witness whereof, I hereunto subscribe my name this 16th day of January, A. D., 1920.

- RAYMOND A. HEISING. 

